Canon's series of L lenses (Luxury lenses) are a professional line of photography lenses made by Canon. Canon has sold zoom and prime L-series lenses for the discontinued FD lens mount, for the current EF lens mount used on all Canon EOS SLR cameras and for the RF mount used on full-frame mirrorless interchangeable-lens cameras. Characteristics Canon L series lenses have a red ring around the lens barrel and the letter "L". Some models of L lenses utilize an infrared reflective heat shield coating. Most L series lenses share a number of common characteristics not found in Canon's line of lower-end lenses. L lenses tend to be more durable, incorporating dust and water-resistant rubber seals on some models. L lenses also contain optics of higher quality, with many lenses containing aspherically ground, fluorite or ultra-low dispersion glass elements. Their front elements do not rotate for the proper operation of some filters, such as circular polarizers. L lenses are often "fast", with maximum apertures commonly 2.8 or 4, and, with the exception of the RF 100–500 mm f/4.5–7.1L IS USM lens, never exceeding 5.6. Standard prime lenses have a much greater maximum aperture, such as Canon's current 50mm and 85mm L lenses which open to 1.2. All current L-series lenses have ultrasonic autofocus motors (USM) and extra communication pins, except for the specialist tilt-shift lenses which do not provide auto focus. Larger sized L-lenses, such as the 70–200 mm, 100–400 mm zooms, and longer focal length primes (300 mm+), usually have an off-white barrel to reduce heat absorption under the sun that may otherwise affect the performance of the lens. Wide angle L-lenses typically have a gelatin filter holder on the mounting collar of the lens, which allows a gelatin to be installed behind the lens. Some telephoto L-lenses, such as the EF 70-200mm zoom lenses, or the EF 300mm f/4L IS USM do not have rear gelatin filter holders. Super-telephoto lenses such as the EF 500mm f/4L IS USM, or the EF 200mm f/2L IS USM have a rear 52mm drop-in filter holder which can be used to hold gelatin type filters. According to Canon, its L series lenses areIncorporating specialized optical materials such as synthetic fluorite, Super UD and UD glass, and large-aperture high-precision aspherical lenses, only lenses that perform to the highest photographic standards are allowed to bear the designation ‘L’. Lenses EF mount zoom lenses EF mount